This invention relates to height and angle adjustable beds in general and more specifically to a bed which is typically found in a hospital or nursing care facility and commonly known in the medical and nursing care industries as a low height adjustable bed or a low bed. A unique aspect of the present invention is its movability in any direction on the floor plane while positioned at any user desired height or angle position. This includes heights which are substantially lower and higher than prior art industry standard low beds and positions such as the Trendelenburg, reverse Trendelenburg, or cardiac chair. The art of the present invention further provides a means for reducing the mechanical actuator force necessary for raising or lowering the bed.
Prior art height and angle adjustable low bed designs provide front and rear lifting and support capabilities and further provide a bed rolling capability when maintained at a specific factory set height. (usually a fully lowered position) The conventional low bed design provides a wide range of bed height positioning including positioning very close to the floor. A typical low bed design further provides one or more support arm mechanisms pivotably attached onto the bed frame which extend near the head or foot of the bed. The support arms help to provide the aforesaid desirable low bed features and may contain rollers, but not castors, which bear upon the plane of the floor near the head or foot of the bed. Said support arms are typically controlled by one or more mechanical or hydraulic linear actuators which cause said support arms to pivot around each bed frame attachment point. Unfortunately, prior art low bed designs require the support arms to be positioned at a specific angle relative to the bed before the bed may be rolled on the floor. That is, typically the prior art bed must be in a fully lowered position before it engages castors mounted on the bed frame and thereby may be rolled on the floor plane.
The present art overcomes the aforesaid limitations of the prior art by utilizing a unique castor base arrangement which allows the user to adjust the height or angle of the bed to any desired level and further roll or move the bed on the two dimensional plane represented by the plane of the floor upon which the bed stands. The present art bed further allows a person to lock the bed and prevent movement in the two-dimensional floor plane at any user desired height or angle.
Prior art beds also require an initial actuator force for raising or lowering the bed which is substantially greater than that of the present art. This occurs due to a mechanical disadvantage presented to the actuators when a low bed is in a nearly or fully lowered position. The present art bed provides an actuator assist spring mechanism which presents an initial force to the bed support arms when the bed is nearly or fully lowered. This initial force helps to overcome the mechanical disadvantage presented to the actuators and thereby reduces the force output required from the actuators.
Accordingly, it is an object of the present invention to provide a low bed that is movable in any direction on the plane of the floor while positioned at a user desired height and/or angle;
Another object of the present invention is to provide a low bed which is stable and position lockable while providing the aforementioned features;
A further object of the present invention is to provide a low bed which utilizes castors instead of rollers while providing the aforementioned features;
A still further object of the present invention is to provide a low bed incorporating one or more actuator assist spring mechanisms which reduce the forces required by the actuators used to raise or lower the bed.
To accomplish the foregoing and other objects of this invention there is provided a height and angle adjustable bed having a rolling base. The apparatus represents an improvement in conventional low bed designs by allowing movement in any direction on the floor plane while the bed is positioned at a user desired height or angle. It also provides an actuator assist spring mechanism which reduces the linear actuator force necessary to raise the bed. In a preferred embodiment the apparatus comprises a bed frame having one or more pivotably attached support arms, one or more castor bases attached to said support arms opposite said bed frame attachment, one or more linear actuators attached between the bed frame and said support arms, and an actuator assist spring mechanism which reduces the linear actuator force necessary for lifting.
The difficulty in providing a two dimensional floor plane bed movement while also maintaining bed stability at a user desired height/angle position is best exemplified by referring to the operation of a typical offset castor wheel. The center mounting axis of a castor wheel as typically used on an office chair is offset from its mounting stud in order to ensure proper tracking when the chair is pushed. That is, if the center axis is not offset, the castor will not have the necessary moment arm of force around its mounting stud axis in order to ensure positioning and tracking of the castor in the direction of applied force. For proper operation, the castor mounting stud must maintain a nearly perpendicular relationship with the floor plane in order to operate properly and avoid premature failure. If a conventional castor is mounted directly onto the end of a low bed support arm, when the arm is moved about its bed frame support axis, the castor stud will not maintain a position which is perpendicular with the floor plane. This non-perpendicular positioning will cause the castor to jam and prohibit the castor from tracking and functioning as expected.
The present art overcomes the aforesaid prior art limitations by placing a pivoting castor base on a base shaft which is mounted onto or between the bed support arms opposite the pivotal attachment points. Each castor base comprises a castor frame with three or more castors which are offset from the axis of the rotating member. That is the three or more castors mounted onto the castor base form a polygonal castor plane, such as a triangle, square, rectangle, etc. which maintains a parallel relationship with the floor plane when in use. A preferred embodiment utilizes four castors in a substantially rectangular configuration with two locking castors.
In a preferred embodiment, the aforesaid base shaft comprises one or more shafts mounted onto a base tube supported by the support arms. The castor base mounted on said shafts is capable of pivoting in the same plane as the pivoting movement of the bed support arms. The offset castors mounted onto the castor base ensures a stable and firm wheeled base for the bed support arms while also allowing the wheeled base to pivot near the end of the bed support arms. Thus, as the bed support arms are lowered or raised, the wheeled base maintains the necessary perpendicular relationship between each castor mounting stud and the floor plane. Since the base has pivoting castors, the bed end having the aforesaid base is able to move easily in any direction on the two dimensional plane of the floor. That is, each castor pivots on its castor mounting stud in order to follow and track in the direction of applied force.
In a preferred embodiment, one or more of the castors contain a castor locking brake which is capable of locking the castor both rotationally and linearly. When locked, the castors prohibit movement of the bed on the floor plane. Nevertheless, when the preferred embodiment includes support arm wheels on the support arms not having the castor base, the bed may be raised or lowered while the castor base is locked. That is, in a preferred embodiment, the support arms near the foot of the bed contain the aforesaid castor base and the support arms near the head of the bed contain support arm wheels.
Another unique feature of the present invention is an actuator assist spring mechanism. As aforesaid, conventional low bed designs typically provide one or more bed support arms pivotably attached to the bed frame. Typically each bed support arm is forceably pivoted on its attachment point axis by a linear mechanical or hydraulic actuator. The linear actuator is typically positioned between a central portion of the support arms and the bed frame near the head or foot portions. As the bed is lowered, the linear actuator pivotably approaches an angle which is nearly parallel with the support arms. This means that only a small portion of the linear actuator force is perpendicular to the plane of the support arms which require rotational movement. That is the perpendicular force is represented by the equation:
Fp=Flsin"THgr" 
where Fp is the force perpendicular to the plane of the actuated support arms, Fl, is the linear actuator force, and "THgr" is the angle between the plane formed by the support arms and the linear actuator. Thus, when the support arms and the linear actuator approach a parallel configuration, "THgr" becomes smaller and approaches zero. This means that a much smaller portion of the linear actuator force Fl, is available to pivot the support arms on their axis. At a lowered position, the linear force needed to raise the support arms can be many times the bed supporting weight thereby necessitating use of a high force actuator.
The present art overcomes the aforementioned high force actuator requirement by incorporating one or more actuator assist spring mechanisms between the bed frame and each support arm. Each assist spring compresses upon bed lowering, thus providing a portion of the lifting force necessary when the bed is raised. The added assist allows the present art low bed to utilize a smaller force linear actuator than would be necessary without the assist spring. In a preferred embodiment, each support arm has an assist arm attached to the support arm near the pivot point with the bed frame. The assist arm acts as the compressing arm for the assist spring mechanism.
The aforementioned frame, support arms, castor base, and associated components may be manufactured from a variety of materials which provide the structural strength necessary. These include but are not limited to materials such as iron, steel, aluminum, titanium, and magnesium along with alloys of such, and plastics, composites, and various woods. The castor and support arm wheels are typically a hard or soft molded plastic or rubber material.